Referring now to FIG. 1, a fluorescent lamp 10 includes a sealed glass tube 12 that contains a first material such as mercury and a first inert gas such as argon, which are both generally identified at 14. The tube 12 is pressurized. Phosphor powder 16 may be coated along an inner surface of the tube 12. The tube 12 includes electrodes 18A and 18B (collectively electrodes 18) that are located at opposite ends of the tube 12. Power is supplied to the electrodes 18 by a control system that may include an AC source 22, a switch 24, a ballast module 26 and a capacitor 28.
When the switch 24 is closed, the control system supplies power to the electrodes 18. Electrons migrate through the gas 14 from one end of the tube 12 to the opposite end. Energy from the flowing electrons changes some of the mercury from a liquid to a gas. As electrons and charged atoms move through the tube 12, some will collide with the gaseous mercury atoms. The collisions excite the atoms and cause electrons to move to a higher state. As the electrons return to a lower energy level they release photons or light. Electrons in mercury atoms release light photons in the ultraviolet wavelength range. The phosphor coating 16 absorbs the ultraviolet photons, which causes electrons in the phosphor coating 16 to jump to a higher level. When the electrons return to a lower energy level, they release photons having a wavelength corresponding to white light.
To send current through the tube 12, the fluorescent light 10 needs free electrons and ions and a difference in charge between the electrodes 18. Generally, there are few ions and free electrons in the gas 14 because atoms typically maintain a neutral charge. When the fluorescent light 10 is turned on, it needs to introduce new free electrons and ions.
The ballast module 26 outputs current through both electrodes 18 during starting. The current flow creates a charge difference between the two electrodes 18. When the fluorescent light 10 is turned on, both electrode filaments heat up very quickly. Electrons are emitted, which ionizes the gas 14 in the tube 12. Once the gas is ionized, the voltage difference between the electrodes 18 establishes an electrical arc. The flowing charged particles excite the mercury atoms, which triggers the illumination process. As more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons and creates more charged particles. Resistance decreases and current increases. The ballast module 26 regulates power both during and after startup.
Referring now to FIG. 2, some ballast modules 50 include a control module 54, one or more electrolytic capacitors 56 and other components 58. The electrolytic capacitors 56 may be used to filter or smooth voltage. Electrolytic capacitors 56 and/or other system components may be sensitive to high operating temperatures. If the operating temperature exceeds a threshold for a sufficient period, the electrolytic capacitor 56 and/or other system components may be damaged and the fluorescent light 10 may become inoperable.